Which inborn error of metabolism prohibits breastfeeding altogether?

Galactosemia is an inborn error of metabolism that prohibits breastfeeding because it involves a deficiency in the enzyme required to metabolize galactose, a sugar found in breast milk and many other dairy products. When an infant with galactosemia consumes breast milk, the galactose present can accumulate in the blood, leading to serious health issues such as liver damage, intellectual disability, and cataracts. For these infants, it is critical to avoid all sources of lactose, which is present in human milk, making breastfeeding inappropriate. Instead, they require a specialized formula that is free from galactose to ensure their health and safety.

In contrast, while conditions like cystic fibrosis, phenylketonuria (PKU), and maple syrup urine disease (MSUD) require specific dietary management, they do not completely prohibit breastfeeding. For instance, infants with PKU can be breastfed but require a low-phenylalanine formula to meet their nutritional needs safely.